Field of the Invention
This invention relates to a fixing device and an image forming apparatus equipped with the fixing device. More specifically, this invention relates to a fixing device equipped with a heat leveling rotating body and a brush rotating body, and an image forming apparatus equipped with the fixing device.
Description of the Related Art
As electrophotography image forming apparatuses, there are an MFP (Multi Function Peripheral) having a scanner function, a facsimile function, a copying function, a function of a printer, a data transmitting function and a server function, a facsimile device, a copying machine, a printer, and so on.
According to generic image forming processes of an image forming apparatus, a surface of an image supporting body is uniformly electrostatic charged by an electrostatic charging device. Then, an expose device exposes the image supporting body in accordance with image information. Herewith, an electrostatic latent image is formed on the surface of the image supporting body. The electrostatic latent image is developed as a toner image, since toner electrostatically adheres to the image supporting body, due to the action of a developing device. The toner image formed on the surface of the image supporting body is transferred onto a secondary transfer belt, and is conveyed to a transfer unit. The toner image on the secondary transfer belt is electrostatically transferred to a sheet conveyed by a sheet conveying unit from a paper feeding tray, by a transfer unit. And then, the sheet is conveyed to a fixing device. In the fixing device, a nip portion between a heating roller and a pressure roller heats the sheet and applies pressure on the sheet, so that the toner image is fixed to the sheet. The sheet on which the toner image was fixed is ejected onto a copy receiving tray by a sheet conveying unit.
Sheets take heat from the fixing device during the fixing in the fixing device, so that temperature decreases at each of portions on which the sheets pass by, of the heating roller and the pressure roller. The temperature decrement causes uniformity of temperature distribution in the axial direction. It may cause fixing failure, for example, uniformity of the gross image or the like. Especially when the sheet is a heavy paper or the like, temperature difference is a lot between a portion on which the sheet passes by and a portion on which the sheet does not pass by. It is going to be more likely that fixing failure occurs.
For example, in Documents 1 and 2 below, a technique for equalizing temperature distribution in an axial direction of a heating roller and a pressure roller by installing a heat leveling roller is proposed.
Document 1 below discloses a heat leveling roller (a heat equalizing roller) in which the outermost layer is a release layer, and a brush roller for cleaning the surface of the heat leveling roller. Temperature of the heat leveling roller is set to be higher than melting temperature of toner. The surface of the heat leveling roller is cleaned, by driving the brush roller rotationally. The heat leveling roller can be located at a pressure contact location and a detached location, with respect to the pressure roller. The brush roller can be located at a contact location and a detached location, with respect to the heat leveling roller.
Document 2 below discloses a technique for placing a web cleaning device in a contact state with respect to a hear leveling roller, and for rotating a belt and a pressure roller, when the heat leveling roller contacts with the belt and the pressure roller. Herewith, remaining toner or the like on the pressure roller is moved to the heat leveling roller side, and cleaned by the web cleaning device. The heat leveling roller is movable, and able to reach a state of contact with the pressure roller and the web cleaning device, and a state of detachment from the pressure roller and the web cleaning device.
Toner and paper powder have a property in which they tend to move from a location having high temperature to a location having low temperature. Therefore, toner and paper powder, which adhered to a heating roller or a pressure roller, tend to transferred to a heat leveling roller. Then, the heat leveling roller tends to get dirty. Hence, conventional fixing devices are provided with a brush roller or a web cleaning device, which contacts with a heat leveling roller to clean a surface of the heat leveling roller, as presented above.